With the rapid development of data services, transport networks of the data services have been significantly developed. A Wavelength Division Multiplexing (Wavelength Division Multiplexing, WDM) system can satisfy the demand for continuously increasing bandwidth required for the data services. An Optical Transport Network (Optical Transport Network, OTN) can provide a solution to flexible scheduling and grooming of wavelengths and sub-wavelengths of the WDM system. Therefore, the OTN is developing gradually. In the OTN, first, an optical signal needs to be converted into an electrical signal through photoelectric conversion, where the most basic electrical signal unit is an Optical Channel Transport Unit (Optical Channel Transport Unit-k, OTUk). The structure of the OTUk includes an Optical Channel Data Unit (Optical Channel Data Unit-k, ODUk) part, and the structure of the ODUk includes an Optical Channel Payload Unit (Optical Channel Payload Unit-k, OPUk) part. Currently, electrical signal units in the case that k=1, 2, 3 exist.
In the OTN, an OTUk signal is transmitted among OTN devices in the network through an OTUk interface. When the OTUk signal is to traverse the network of an operator, data in the OTUk signal needs to be transparently transmitted, and no modification can be performed on the data of the OTUk signal. In the prior art, in order to ensure transparent transmission of the data in the OTUk signal, first, the OTUk signal is unwrapped into an ODUk signal; then, the ODUk signal is transparently transmitted end-to-end; and afterward, the ODUk signal is wrapped into an OTUk signal. It can be seen from the preceding procedure that, in the prior art, only an ODUk signal is transparently transmitted, and fully transparent transmission of an OTUk signal cannot be implemented.